But TBH I never hear anyone say it in that meaning, at least in my region we only use 'dawaj' or 'dajesz' as an encouragement.

Boy so many years out of the country and I am not sure anymore what is common Polish expression and what is not. Having said that am I wrong thinking that "Trzymaj" which literally means "Hold" was used as encouragement when someone was on right course to success, but he or she just needed to continue to do what they were doing so far, in other words hold current course of action?

The best of luck to all tennis players; The game is on!
-AndreP.S.Well,... special luck to Agnieszka Radwanska, Marta Domachowska, Daniela Hantuchova, Urszula Radwanska